Piezo-electric resonator



y 932. w. A. MARRISON PIEZO ELECTRIC RESNATOR Filed May ll, 1928 Fle. 2.

/NVENTOR By %ARRL-WWA! v a Chemical solvent, for example, hydrofluoric'Patented July 26, 1932 UNITED STATES PATENT OFFICE WABREN A. IARBISON,OF OBANGE, NEW JERSEY, ASSIGNOR TO BELL 'TELEPEONE LABORATOBIES,INCOBPOBATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORKPIEZO-ELECTRIC RESONATOR Application med-Ka 1928. Serial No. 27 7317.

This invention relates to piezo-electric crystal resonators and moreparticularlyto.

a method of adjusting them to operate at a desired frequency.

An object of the inventionis to secure a very hi 'hdegree of precisionin the' adjustment o? piezo-electric crystals, so thatthey willoscillate at a desired frequency.

Another object is to produce crystals having uniform contact surfaces,thcreby avoiding irregularities in their activity and in the frequencyat which they will oscillate.

A further object of the inventionis to provide means for facilitatingthe selection of ood resonators.

t present, piezo-electric resonators such as quartz resonators, forexample, are adjusted for frequency by lapping, e., by slowly grindingone surface of the resonator with a fine-abrasive. In the use of thismethod abrupt variations, in the surface of the crystal frequentlyoccur. These variations atfect its activity and the frequency at whichit oscillates.

In accordance with the present invention acid, is used to dissolvematerial from the surface of a Crystal to produce an etched surfacewhich is free from irregularities. Commercal hydrofiuoric acid may beused and the length of exposure depends on the change in the Crystalnecessary to render it resonant to the desired frequency. The change infrequency, obtaned for a given shape of resonator and given temperatureand concentration of the solvent is believed to be approximatelydirectly proportional to the length of exposure.

In the drawing: v

Fig. l is a piezo-electric resonator which has been cut' from a naturalcrystal to such dimensions as to have approximately the desiredresonance frequency.

Fig. 2 illustrates the process disclosed herein and shows the resonator1 immersed in hydrofiuoric acid 2 contained in a suitable container or.beaker 3, as of lead.

Fig. 3 is a View of the resonator after being adjusted to the desiredfrequency by exposure to the acid.

Advantages of chenical treatment of crystals are that material isremoved from 'the entire surface of the crystal to render it uniform,and the Crystal may be very precisely adjusted`to oscillatc at aselected frequency.

As in the past, the resonating element is cut from the natural Crystal,its dimensions being. slightly greater than those necessary to itsvibrat-ion at the desired frequency. In cutting from the naturalcrystal, irregularities are likely to occur in the surfaces. TheChemical solvent to which the element is exposed, serves to dissolve theirregularities and if necessary toits reduction to'the properdinensions, a nitnrm layer is dissolved from the surfacesof the element.The dimensions of the element are precisely adjusted to a value suchthat it will' vibrate at the desired frequency.

In order to deternine whether a crystal was free from' twinning whenprepared by the method heretofore practiced, it has been necessary tocut the 'esonator to the size desired for use, polish the resonator, andto examine it with special optical apparatus.

With the present method the crude Crystal is cut into slabs of largedimensions from which a number of resonators may be'cut. The slab isthen exposed to the action of a Chemical solvent toproduce an etchedsurface, whereby defects, notably twinning, are rendered visible to theunaided sight. A sec-- tion of the slab 'is then selected which isfreethen exposed to the action of the Chemical solvent until it isreduced to such dimensions they have been brought to the finished state.

WVhat is claimed is: 1. The method of producing a quartz crys-Consequently' it pro- Vides a method for selecting crystals before' 'talelement which omprises cutting the crystal element to theapproXimate-size and dissolving a portion of said Crystal element withhydrofiuoric acid.

2. The method of'adjusting a quartz crystal element to a desired sizewhich comprises treating said Crystal element with hydrofluoric acid.

3. A quartz crystal resonator having a substantially uniform chemicallyetched surface.

tal element having uniform contact surfaces,

which comprises treating a quartz Crystal element with a substance whichis a Chemical solvent for the Crystal.

' 5. The method of producing a piczo-electrically active quartz elementwhich comprises cutting a slab from a natural quartz Crystal havingpiezo-electric properties, exposing the slab to the action of a Chemicalsolvent whereby defects in the slab are readily 'dctectable and cuttinga resonator' from a section which is free from defects.

6. The method of producing a piezo-electrically active quartz elementwhich comprises cutting a slab from a natural quartz Crystal havingpiezo-electric properties and. cxposing said slab to the action ofhydrofiuoric acid. r

In witness whereof, I hereunto subscribe my name this 10th day of May,1928.

WARREN A. MARRISON.

4. The method of producing a quarrtz crys-'

